1. Field of the Invention
The present invention relates to a camera and, more particularly, to an arrangement for preventing the positional deviations of photographed frames of a film.
2. Description of the Related Art
If a vibration is applied to a camera placed in a photography standby state, the film accommodated in the camera travels owing to the vibration and causes a number of problems such as a deviation in the positional relationship between the perforations of the film and photographed frames or an overlap of adjacent photographed frames which occurs if the film travels to a large extent.
There are film cartridges of the type which have a film egress/ingress slot provided with a movable light-shielding door. Unlike existing popular film cartridges, this type of film cartridge has a structure in which the film egress/ingress slot is not provided with a light-shielding member made of pile fabric and, therefore, gives no resistance to the film of the film cartridge. In such a film cartridge, a film travel is easily caused by a vibration, and the amount of film travel due to the vibration is large.
The following proposals have been made with respect to a method of preventing the aforesaid travel of the film due to a vibration. Each of the proposals is intended to realize stop control of the film by inserting a claw into a perforation formed in the film.
(i) U.S. Pat. No. 4,903,061 proposes the art of retracting the claw from a film running path during prewinding.
(ii) U.S. Pat. No. 4,914,462 proposes the art of inhibiting the claw from being inserted into a perforation formed in the leader end of the film, during the thrust operation of feeding the film from the film egress/ingress slot for the purpose of automatic loading from a case (film cartridge) in which the film is completely accommodated.
Japanese Laid-Open Patent Application No. Sho 58-125029 and others propose the art of providing a winding stop in a film driving mechanism to perform stop control of the film by engaging the film driving mechanism each time the film is advanced by one frame.
Further, in a camera of the type which performs photography each time the film is wound up by one frame, even if only the take-up spool of the camera or both of the take-up spool of the camera and the cartridge spool are engaged, the film travels in the film winding direction when a vibration is applied to the camera, because although the film is tightly wound around the take-up spool of the camera, it is wound around the cartridge spool in a coil with a certain extent of looseness.
There are also cameras of the type which uses a film having a magnetic recording portion. In this type of camera, during film transport, a magnetic head is brought into abutment with such film to magnetically write or read photography information or the like on or from the film.
However, such a camera has the problems that if the magnetic head is in abutment with the film during photography, the flatness of the film is impaired, and that if the magnetic head remains in contact with the film for a long time, the film may stick to the magnetic head.
To solve the problems, the following proposals have been made with respect to a mechanism for maintaining the magnetic head in abutment with the film only during the writing and reading of magnetic information and normally keeping the magnetic head and the film away from each other.
(i) Japanese Laid-Open Patent Application No. Hei 3-200131 proposes the art of bringing the magnetic head into abutment with the film by a dedicated motor when photography information is to be magnetically written, and normally keeping the magnetic head retracted from the film.
(ii) Japanese Laid-Open Patent Application No. Hei 5-150321 proposes the art of retracting a pressure pad for pressing the film against the magnetic head (hereinafter referred to simply as the pad) in interlocking relation to the operation of the film driving mechanism or a barrier or to a film-cartridge loading operation.
(iii) Japanese Laid-Open Patent Application No. Hei 5-165091 proposes the art of moving backward and forward the magnetic head in interlocking relation to a photographing member, such as a mirror or a shutter charging member, or moving backward and forward the magnetic head by a solenoid plunger.
(iv) Japanese Laid-Open Patent Application No. Hei 3-289639 proposes the art of moving backward and forward the magnetic head by means of a film transporting motor and an electromagnet.
(v) Japanese Laid-Open Patent Application No. Hei 4-68334 proposes the art of normally urging the magnetic head in a direction away from the film and, only during the running of the film, maintaining the magnetic head in abutment with the film by the power of a film running motor.
(vi) Japanese Laid-Open Patent Application No. Hei 6-35060 proposes the art of moving forward and backward the pad for pressing the film against the magnetic head, by means of a cam contained in a gear train for film transport.
(vii) Japanese Laid-Open Patent Application No. Hei 7-92550 proposes the art of moving the magnetic head by means of a motor for charging a mechanism such as a mirror and a shutter.
In each of the mechanisms disclosed in U.S. Pat. Nos. 4,903,061 and 4,914,462, since the claw is inserted into a perforation of the film, it is possible to prevent the film from travelling in either of the film winding and rewinding directions owing to a vibration. To insert the claw into a perforation of the film, it is necessary to stop the film with high accuracy before the insertion of the claw into the perforation. However, actually, the stop position of each perforation varies depending on the normal stopping accuracy of the film, so that it is very difficult to accurately insert the claw into the perforation.
For this reason, in such a system, it is extremely difficult to prevent the film from travelling in either of the film winding and rewinding directions owing to a vibration.
In addition, the respective conventional examples (summarized below as arrangements (a), (b) and (c)) are merely proposals which are independent of each other:
(a) the arrangement for inserting the claw into a perforation of the film, PA1 (b) the arrangement for engaging the film driving mechanism, and PA1 (c) the arrangement for moving backward and forward the magnetic head or the pad.
If the arrangements (a) to (c) are combined, the following problems occur.
(i) The structure becomes complicated.
(ii) The timing of the operation of each of the arrangements (a) to (c) is difficult to adjust.
(iii) Although each of the arrangements (a) to (c) individually serves to prevent the travel of the film, all of them become inoperative at a particular timing of the operation of each of the arrangements (a) to (c). At this time, the film becomes free, i.e., the travel of the film is not restricted, so that if a vibration or the like occurs, the film easily travels.
(iv) When each of the arrangements (a) to (c) operates, unnecessary force is applied to the film.